[clang][Interp] Don't return success for already failed global variables

We might be visiting them more than once. We used to return true for
second and subsequent cases, just because we had already visited it
before.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -2510,6 +2510,12 @@ template <class Emitter>
 bool ByteCodeExprGen<Emitter>::visitDecl(const VarDecl *VD) {
   assert(!VD->isInvalidDecl() && "Trying to constant evaluate an invalid decl");
 
+  // Global variable we've already seen but that's uninitialized means
+  // evaluating the initializer failed. Just return failure.
+  if (std::optional<unsigned> Index = P.getGlobal(VD);
+      Index && !P.getPtrGlobal(*Index).isInitialized())
+    return false;
+
   // Create and initialize the variable.
   if (!this->visitVarDecl(VD))
     return false;

clang/test/SemaCXX/PR20334-std_initializer_list_diagnosis_assertion.cpp

@@ -1,5 +1,8 @@
 // RUN: %clang_cc1 -std=c++11 -verify -emit-llvm-only %s
 // RUN: %clang_cc1 -std=c++98 -fsyntax-only -verify %s -DCPP98
+// RUN: %clang_cc1 -std=c++11 -verify -emit-llvm-only %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++98 -fsyntax-only -verify %s -DCPP98 -fexperimental-new-constant-interpreter
+
 
 namespace std {
   template <class _E>